EPILEPTOGENIC SPIKES AND SEIZURES BUT NOT HIGH-VOLTAGE SPINDLES ARE INDUCED BY LOCAL FRONTAL CORTICAL APPLICATION OF GAMMA-HYDROXYBUTYRATE

Combining the methods of microdialysis and EEG recording, we have exam ined the effect of unilaterally, intracortically applied gamma-hydroxy butyrate (GHB) on frontal cortical EEG activity in freely moving rats. GHB, a natural endogenous GABA metabolite, is known to induce rhythmi c spike and wave activity, resembling generalized petit mal epilepsy. Without GHB, spontaneous high voltage spindles (HVS, 6-9 Hz) were obse rved during awake and immobile behavior in most of the animals (HVS ra ts), while others never had any HVS. In those both groups of animals i ntracortical application of GHB induced epileptogenic spikes (< 0.5 Hz ) behaviorally accompanied by occasional myoclonic jerks and epileptic discharges (< 2 Hz) with behavioral convulsions and contraversive mov ements towards the left hindlimb (seizures) but did not induce HVS or spike and waves, as reported after systemic application. In the group of rats with spontaneous occurring HVS the amplitude of the HVS on the side of the microdialysis probe was suppressed by GHB and GHB-induced spikes invading the contralateral cortex frequently triggered and ter minated local HVS. The results point to different neural mechanisms fo r the generation of HVS and spikes and epileptic discharges (seizures) induced after local intracortical application of GHB.